Port 587: SMTP submission
Authenticated mail submission with STARTTLS.
- Port
- 587
- Protocol
- TCP
- Service
- SMTP submission
- Exposure
- Expose only with access controls
What is port 587 used for?
Mail clients sending outgoing mail.
Is it safe to expose port 587 to the internet?
Require authentication and TLS.
If port 587 seems closed or unreachable
- Check that the SMTP submission service is running and listening on port 587, not only on 127.0.0.1.
- Check the firewall on the host itself (Windows Defender Firewall, iptables, nftables, ufw) for a rule that allows TCP 587.
- If the host is behind a router, confirm the forwarding rule points to the correct internal address and that your internet provider does not use carrier-grade NAT.
- Test from outside your own network. A port can be open locally and blocked at the edge, or the other way round.
Using port 587 safely
Port 587 can be exposed when the host exists to provide this service, but add controls: restrict source addresses where you can, require strong authentication and encryption, and monitor the logs for repeated failures.
Check whether port 587 is open on your host
The check connects from our server, so it shows what the internet can reach.
Open the port checker